Thin-walled, extensible articles such as gloves and other medical products have long been made from natural latex polymers. Typically, such articles are formed from natural rubber latex, a naturally occurring emulsion of polymer and water, with added stabilizing agents and vulcanizing chemicals. In order to produce the articles, a former having the shape of the article to be formed is first coated with a coagulating solution. After the coagulating solution is applied, the former is dipped into a latex mixture once or several times to build up a layer of the desired thickness. The film is allowed to dry and then vulcanized to provide adequate mechanical and physical properties.
Natural latex polymers have many advantages in these applications, being strong and highly elastic and having good overall tactile properties. The good tactility is believed to be a result of the natural latex having low deformation stress at ten to five hundred percent elongations and high elastic recovery.
Even though natural latex offers various advantages, those skilled in the art have been attempting to create an extensible article from synthetic polymers that have physical properties similar to natural latex. In this regard, various types of synthetic elastomeric polymer products have been developed for use in thin articles produced by dip forming. For example, nitrile polymers are commonly used for this purpose. Further, U.S. Pat. Nos. 5,112,900 and 5,407,715 both disclose elastomeric triblock copolymer compositions for producing elastomeric articles. Both of the above patents are incorporated herein by reference.
The various synthetic polymer compositions that have been developed to date have properties very comparable to natural latex polymers. Further, articles formed from the synthetic compositions have been found to possess very uniform film thicknesses without an appreciable formation of pinholes.
A need still remains, however, for improved elastomeric articles, such as gloves, that are made from other types of synthetic polymers. The present invention fulfills this need, and further provides related advantages.
In general, the present invention is directed to elastomeric articles, such as gloves and condoms. The articles are made from a thin film having elastic properties. The film is produced from a synthetic polymer. The synthetic polymer can be, for instance, BARRIERPRO BP 2000 sold by Riechold Chemicals, Inc. BARRIERPRO BP 2000 contains TYLAC 68080 polymer.
According to the present invention, the synthetic polymer is cross-linked with a metal oxide cross-linking agent. The cross-linking agent, for instance, may be zinc oxide, magnesium oxide, cadmium oxide, and the like. The cross-linking agent can be present in the polymer in an amount from about 0.25 PHR to about 3 PHR. (Parts per hundred rubber).
Of particular importance, the present inventors discovered that elastomeric articles can be formed from the above-described polymers without using conventional sulphur-containing cross-linking agents and accelerators. In fact, the use of an accelerator is not required. In the past, when using sulphur-containing cross-linking agents and accelerators, the polymer typically had to be cured at temperatures greater than about 130xc2x0 C. When using a metal oxide as the cross-linking agent, however, the synthetic polymer emulsion can be cured at temperatures less than about 120xc2x0 C., particularly at temperatures less than 100xc2x0 C. and more particularly at temperatures less than 85xc2x0 C.
The resulting polymer is sulfur-free. As used herein, the term xe2x80x9csulfur-freexe2x80x9d is defined as a polymer or a polymer emulsion that contains no measurable amounts of elemental sulphur or sulfur compounds.
In producing elastomeric articles in accordance with the present invention, such as gloves and condoms, a former in a desired shape is first preheated. Once preheated, the former is dipped or immersed into a coagulant bath. The former is withdrawn from the coagulant bath and then dried leaving a coagulant, such as calcium nitrate, on the surface of the former.
Next, the former is dipped into a polymer emulsion. In accordance with the present invention, the emulsion contains a synthetic polymer, water, and a metal oxide cross-linking agent, such as zinc oxide. The coagulant-coated former is dipped or immersed into the emulsion and withdrawn leaving a coating of the polymer emulsion on the former. The polymer coating on the former is then polymerized and dried at temperatures less than about 130xc2x0 C., particularly at temperatures less than about 100xc2x0 C.
Once the polymer coating is dried on the former, the elastomeric article can be removed from the former or the former can be once again dipped into the emulsion for increasing the thickness of the coating.
Other features and aspects of the present invention are discussed in greater detail below.